Power was born on the 13th of November, 1976, in Cork, Ireland, and is a distant cousin of Irish actor Tyrone Power. Power's great-grandfather was Sir John Power, Member of Parliament for Wimbledon before the Second World War.
Power started acting from an early age; her very first TV appearance was on a chicken nuggets advertisement. She attended the Sylvia Young Theatre School in Marylebone.
Her early TV appearances included parts in Bonjour La Classe (1993) and Moonacre (1993) for the BBC, a part which involved horse-riding. Other early roles included The Manageress for Channel 4 (1990).
She made her stage debut in the theatrical adaptation of The Prime of Miss Jean Brodie at the National Theatre in 1998. Her voice was featured in the English dubbed version of Alice. She was a regular cast member on Yorkshire Television soap opera Emmerdale as Jessica McAllister for two years. She also had a small role in the television show Murder In Mind.
In 2006, she appeared in the BBC drama Waterloo Road as English teacher Lorna Dickey, and returned for the second series in 2007, until her character committed suicide having been diagnosed with multiple sclerosis.
In early 2008, she starred in a Torchwood (episode: "From Out of the Rain") as Pearl, a circus star who escapes an old cinema film and seeks revenge on those who put her out of business.
Power was seen in the British action movie The Tournament as the ruthless assistant to Liam Cunningham's Tournament Master. In 2012, she appeared in two episodes of ITV drama Whitechapel.